Rotate asynchronously?

[koorgoo]

There are 4 files a a.1 a.2 a.3.

Phase 1 (sync) - rename a -> a.0 and write to newly created a.
Phase 2 (async) - remove a.3 and rename a.1 a.2 -> a.2 a.3.

Potential problems:

• Program exists unexpectedly. rotate.File.Sync must wait for phase 2.